A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifl... more A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifluoroethylene) copolymer P(VDF-TrFE) and ferroelectric ceramics of barium lead zirconate titanate (BPZT) solid solution is presented in this work. The composite films containing up to 50 vol.% of BPZT grains with size [Formula: see text]1[Formula: see text][Formula: see text]m were prepared by the solvent cast method. Frequency dependences of real and imaginary components of the complex permittivity were determined. The concentration dependence of the dielectric constant was discussed.
This chapter introduces the structural background of the appearance of polar nanoregions in relax... more This chapter introduces the structural background of the appearance of polar nanoregions in relaxors, describes their major macroscopic dielectric and ferroelectric properties, and presents the results of recent investigations of local polar structures by piezoresponse force microscopy (PFM). Statistical analysis of observed nanodomains, their temperature evolution, and polarization switching results are given for several relaxor families based on Sr x Ba1–x Nb2O6 (SBN), PbMg1/3Nb2/3O3 (PMN), PbZn1/3Nb2/3O3 (PZN), and (Pb1–x La x )(Zr1–y Ti y )O3 (PLZT). The PFM technique has proved to be a powerful tool for the investigation of local properties of relaxors where optical techniques obviously fail because of their lack of resolution. In addition, size- and grain boundary-dependent phenomena in relaxors are reviewed for representative PLZT compositions. Examples of investigations of polar structures in relaxor films and ceramics and single are also presented.
Solid solutions of (1 − x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 promise to exhibit a large electroca... more Solid solutions of (1 − x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 promise to exhibit a large electrocaloric effect (ECE), because their Curie temperature and a multiphase coexistence region lie near room temperature. We report on direct measurements of the electrocaloric effect in bulk ceramics 0.65Ba(Zr0.2Ti0.8)O3-0.35(Ba0.7Ca0.3)TiO3 using a modified differential scanning calorimeter. The adiabatic temperature change reaches a value of ΔTEC = 0.33 K at ∼65 °C under an electric field of 20 kV/cm. It remains sizeable in a broad temperature interval above this temperature. Direct measurements of the ECE proved that the temperature change exceeds the indirect estimates derived from Maxwell relations by about ∼50%. The discrepancy is attributed to the relaxor character of this material.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
ABSTRACT The roughness in GaN/InGaN thin films and multilayers was studied with Rutherford backsc... more ABSTRACT The roughness in GaN/InGaN thin films and multilayers was studied with Rutherford backscattering (RBS). Quantitative data analysis, including the determination of the roughness parameters, was made through the application of models developed for specific kinds of roughness and/or intermixing. In a first step, the assumptions made in the development of the models were tested, and their limits of validity were established. In all cases, the models are valid for relatively small aspect ratios of the interface or surface structures analysed, and the roughness parameters should follow a Gaussian distribution. Within their limits of application and validity, the models used in the RBS data analysis are general, and can be used in the study of any given system. The RBS results for GaN/InGaN thin films were compared to atomic force microscopy (AFM) and scanning electron microscopy experiments. In the samples within the application range of the models, excellent agreement was found between the roughness determined by RBS and the surface roughness measured with AFM for thin films. Finally, in GaN/InGaN multiple quantum wells, the roughness/intermixing was found to increase with both the well composition and the number of wells grown in the stack, due to a deterioration of the structural quality with the amount of strain incorporated in the structure. (C) 2003 Elsevier B.V. All rights reserved.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2010
Film deposition of Ni2MnGa phaselike alloy by radio frequency (rf) magnetron sputtering was perfo... more Film deposition of Ni2MnGa phaselike alloy by radio frequency (rf) magnetron sputtering was performed onto bare Si(100) substrates and LaNiO3∕Pb(Ti,Zr)O3 (LNO/PZT) ferroelectric buffer layer near room temperature. The prepared samples were characterized using conventional x-ray diffraction (XRD), superconducting quantum interference device, and electron dispersive x-ray spectroscopy from scanning electron microscope observations. The optimized films deposited under high rf power and low argon pressure present good surface quality and highly textured phase crystallization. The positioning distance between the substrate and the target-holder axis has some limited effect on the film’s composition due to the specific diffusion behavior of each element in the sputtering plasma. Extended four pole high resolution XRD analysis allowed one to discriminate the intended Ni–Mn–Ga tetragonal martensitic phase induced by the (100) LNO/PZT oriented buffer. This low temperature process appears to ...
Polycrystalline samples with the nominal composition Bi0.8Pb0.2FeO3 have been studied via x-ray d... more Polycrystalline samples with the nominal composition Bi0.8Pb0.2FeO3 have been studied via x-ray diffraction, Mössbauer spectroscopy, dielectric, magnetic, and local ferroelectric measurements. It has been found that the heterovalent Pb2+ substitution in Bi0.8Pb0.2FeOy is realized through the formation of oxygen vacancies. The crystal structure of the compound has been shown to be described by the non-centrosymmetric space group R3c. Investigations of local ferroelectric and magnetic properties have confirmed that spontaneous polarization and weak ferromagnetism coexist in this material at room temperature. The nature of the weak ferromagnetic moment in this compound is discussed in terms of a doping-induced change in the magnetic anisotropy.
Extending the framework for multiferroic materials, in which long-range electric and magnetic ord... more Extending the framework for multiferroic materials, in which long-range electric and magnetic orderings coexist, we present a novel 'multiglass' concept, where two different glassy states occur simultaneously. It applies to Sr0.98Mn0.02TiO3 ceramics, where the Mn2+ dopant ions are at the origin of both polar and spin glasses. Spin freezing is initiated at the dipolar glass temperature, Tg≈38 K. Below Tg, both glass phases are independently verified by memory and rejuvenation effects. Strong biquadratic interaction of the Mn2+ spins with the optic soft mode of the incipient ferroelectric host crystal SrTiO3 explains the high spin glass temperature and comparably strong higher order magnetoelectric coupling between the polar and magnetic degrees of freedom.
The effect of heterovalent B-site doping on ergodicity of relaxor ferroelectrics is studied using... more The effect of heterovalent B-site doping on ergodicity of relaxor ferroelectrics is studied using (1 − y)(0.81Bi1/2Na1/2TiO3-0.19Bi1/2K1/2TiO3)-yBiZn1/2Ti1/2O3 (BNT-BKT-BZT) with y = {0.02;0.03;0.04} as a model system. Both the large- and small-signal parameters are studied as a function of electric field. The crystal structure is assessed by means of neutron diffraction in the initial state and after exposure to a high electric field. In order to measure ferroelastic domain textures, diffraction patterns of the poled samples are collected as a function of sample rotation angle. Piezoresponse force microscopy (PFM) is employed to probe the microstructure for polar regions at a nanoscopic scale. For low electric fields E < 2 kV·mm−1, large- and small-signal constitutive behavior do not change with composition. At high electric fields, however, drastic differences are observed due to a field-induced phase transition into a long-range ordered state. It is hypothesized that increasin...
We present results of piezoresponse force microscopy studies on “uniaxial” relaxors SrxBa1− xNb2O... more We present results of piezoresponse force microscopy studies on “uniaxial” relaxors SrxBa1− xNb2O6 (SBN) and on “cubic” relaxors Pb[Mg1/3Nb2/3]1− xTixO3 (PMN-PT). The chosen compositions exhibit a spontaneous transition from the ergodic relaxor into the ferroelectric state. In both materials static regions of non-zero piezoresponse were found above the corresponding transition temperature. We attribute them to large polar nanosized regions (PNRs),
A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifl... more A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifluoroethylene) copolymer P(VDF-TrFE) and ferroelectric ceramics of barium lead zirconate titanate (BPZT) solid solution is presented in this work. The composite films containing up to 50 vol.% of BPZT grains with size [Formula: see text]1[Formula: see text][Formula: see text]m were prepared by the solvent cast method. Frequency dependences of real and imaginary components of the complex permittivity were determined. The concentration dependence of the dielectric constant was discussed.
This chapter introduces the structural background of the appearance of polar nanoregions in relax... more This chapter introduces the structural background of the appearance of polar nanoregions in relaxors, describes their major macroscopic dielectric and ferroelectric properties, and presents the results of recent investigations of local polar structures by piezoresponse force microscopy (PFM). Statistical analysis of observed nanodomains, their temperature evolution, and polarization switching results are given for several relaxor families based on Sr x Ba1–x Nb2O6 (SBN), PbMg1/3Nb2/3O3 (PMN), PbZn1/3Nb2/3O3 (PZN), and (Pb1–x La x )(Zr1–y Ti y )O3 (PLZT). The PFM technique has proved to be a powerful tool for the investigation of local properties of relaxors where optical techniques obviously fail because of their lack of resolution. In addition, size- and grain boundary-dependent phenomena in relaxors are reviewed for representative PLZT compositions. Examples of investigations of polar structures in relaxor films and ceramics and single are also presented.
Solid solutions of (1 − x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 promise to exhibit a large electroca... more Solid solutions of (1 − x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 promise to exhibit a large electrocaloric effect (ECE), because their Curie temperature and a multiphase coexistence region lie near room temperature. We report on direct measurements of the electrocaloric effect in bulk ceramics 0.65Ba(Zr0.2Ti0.8)O3-0.35(Ba0.7Ca0.3)TiO3 using a modified differential scanning calorimeter. The adiabatic temperature change reaches a value of ΔTEC = 0.33 K at ∼65 °C under an electric field of 20 kV/cm. It remains sizeable in a broad temperature interval above this temperature. Direct measurements of the ECE proved that the temperature change exceeds the indirect estimates derived from Maxwell relations by about ∼50%. The discrepancy is attributed to the relaxor character of this material.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
ABSTRACT The roughness in GaN/InGaN thin films and multilayers was studied with Rutherford backsc... more ABSTRACT The roughness in GaN/InGaN thin films and multilayers was studied with Rutherford backscattering (RBS). Quantitative data analysis, including the determination of the roughness parameters, was made through the application of models developed for specific kinds of roughness and/or intermixing. In a first step, the assumptions made in the development of the models were tested, and their limits of validity were established. In all cases, the models are valid for relatively small aspect ratios of the interface or surface structures analysed, and the roughness parameters should follow a Gaussian distribution. Within their limits of application and validity, the models used in the RBS data analysis are general, and can be used in the study of any given system. The RBS results for GaN/InGaN thin films were compared to atomic force microscopy (AFM) and scanning electron microscopy experiments. In the samples within the application range of the models, excellent agreement was found between the roughness determined by RBS and the surface roughness measured with AFM for thin films. Finally, in GaN/InGaN multiple quantum wells, the roughness/intermixing was found to increase with both the well composition and the number of wells grown in the stack, due to a deterioration of the structural quality with the amount of strain incorporated in the structure. (C) 2003 Elsevier B.V. All rights reserved.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2010
Film deposition of Ni2MnGa phaselike alloy by radio frequency (rf) magnetron sputtering was perfo... more Film deposition of Ni2MnGa phaselike alloy by radio frequency (rf) magnetron sputtering was performed onto bare Si(100) substrates and LaNiO3∕Pb(Ti,Zr)O3 (LNO/PZT) ferroelectric buffer layer near room temperature. The prepared samples were characterized using conventional x-ray diffraction (XRD), superconducting quantum interference device, and electron dispersive x-ray spectroscopy from scanning electron microscope observations. The optimized films deposited under high rf power and low argon pressure present good surface quality and highly textured phase crystallization. The positioning distance between the substrate and the target-holder axis has some limited effect on the film’s composition due to the specific diffusion behavior of each element in the sputtering plasma. Extended four pole high resolution XRD analysis allowed one to discriminate the intended Ni–Mn–Ga tetragonal martensitic phase induced by the (100) LNO/PZT oriented buffer. This low temperature process appears to ...
Polycrystalline samples with the nominal composition Bi0.8Pb0.2FeO3 have been studied via x-ray d... more Polycrystalline samples with the nominal composition Bi0.8Pb0.2FeO3 have been studied via x-ray diffraction, Mössbauer spectroscopy, dielectric, magnetic, and local ferroelectric measurements. It has been found that the heterovalent Pb2+ substitution in Bi0.8Pb0.2FeOy is realized through the formation of oxygen vacancies. The crystal structure of the compound has been shown to be described by the non-centrosymmetric space group R3c. Investigations of local ferroelectric and magnetic properties have confirmed that spontaneous polarization and weak ferromagnetism coexist in this material at room temperature. The nature of the weak ferromagnetic moment in this compound is discussed in terms of a doping-induced change in the magnetic anisotropy.
Extending the framework for multiferroic materials, in which long-range electric and magnetic ord... more Extending the framework for multiferroic materials, in which long-range electric and magnetic orderings coexist, we present a novel 'multiglass' concept, where two different glassy states occur simultaneously. It applies to Sr0.98Mn0.02TiO3 ceramics, where the Mn2+ dopant ions are at the origin of both polar and spin glasses. Spin freezing is initiated at the dipolar glass temperature, Tg&ap;38 K. Below Tg, both glass phases are independently verified by memory and rejuvenation effects. Strong biquadratic interaction of the Mn2+ spins with the optic soft mode of the incipient ferroelectric host crystal SrTiO3 explains the high spin glass temperature and comparably strong higher order magnetoelectric coupling between the polar and magnetic degrees of freedom.
The effect of heterovalent B-site doping on ergodicity of relaxor ferroelectrics is studied using... more The effect of heterovalent B-site doping on ergodicity of relaxor ferroelectrics is studied using (1 − y)(0.81Bi1/2Na1/2TiO3-0.19Bi1/2K1/2TiO3)-yBiZn1/2Ti1/2O3 (BNT-BKT-BZT) with y = {0.02;0.03;0.04} as a model system. Both the large- and small-signal parameters are studied as a function of electric field. The crystal structure is assessed by means of neutron diffraction in the initial state and after exposure to a high electric field. In order to measure ferroelastic domain textures, diffraction patterns of the poled samples are collected as a function of sample rotation angle. Piezoresponse force microscopy (PFM) is employed to probe the microstructure for polar regions at a nanoscopic scale. For low electric fields E < 2 kV·mm−1, large- and small-signal constitutive behavior do not change with composition. At high electric fields, however, drastic differences are observed due to a field-induced phase transition into a long-range ordered state. It is hypothesized that increasin...
We present results of piezoresponse force microscopy studies on “uniaxial” relaxors SrxBa1− xNb2O... more We present results of piezoresponse force microscopy studies on “uniaxial” relaxors SrxBa1− xNb2O6 (SBN) and on “cubic” relaxors Pb[Mg1/3Nb2/3]1− xTixO3 (PMN-PT). The chosen compositions exhibit a spontaneous transition from the ergodic relaxor into the ferroelectric state. In both materials static regions of non-zero piezoresponse were found above the corresponding transition temperature. We attribute them to large polar nanosized regions (PNRs),
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